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Anal fistula surgery

Expert reviewer, Mr. Nick Reay-Jones, Consultant Surgeon General Surgery
Next review due February 2025

An anal fistula is a small tunnel that develops between the skin around your bottom (anus) and the very end of your anal canal (see the image below). You’ll usually need to have surgery to treat an anal fistula.

Image showing the large and small bowels

About anal fistula

An anal fistula can develop if you’ve had an infection of the glands around your bottom (anus). The infection can cause an abscess (a collection of pus) between your skin and anus. When the pus drains away, it may leave a small tunnel (the fistula) behind.

Around a third of people with an abscess in their anus go on to develop a fistula. An anal fistula can also be caused by long-term bowel conditions, such as Crohn’s disease.

A fistula is usually a tunnel between your skin and your anal canal. But sometimes, additional tracts can develop from the same tunnel, or it can pass through the muscles of your anus (your sphincter muscles). These are known as complex anal fistulas and can be more difficult to treat.

Anal fistula treatment is usually surgery – they don’t usually heal by themselves, and without treatment, they can lead to repeated abscesses.

Symptoms of anal fistula

Anal fistula symptoms can include:

  • discharge from the opening of the fistula in your skin, which you may feel as a hole or lump – this may have pus or blood in it
  • pain, discomfort and swelling in and around your bottom (anus)
  • diarrhoea
  • irritated skin around your bottom (anus)

These symptoms aren't always caused by an anal fistula, but if you have them, see your GP.

Diagnosis of anal fistula

Your GP will ask about your symptoms and may examine you. Your GP may be able to see the opening of an anal fistula in the skin around your bottom (anus), which is known as the external opening. They may check for further signs by gently inserting their finger inside your bottom. Your GP may refer you to a colorectal surgeon for further investigation and treatment.

Your surgeon may need to do some additional tests and examinations if the diagnosis isn’t clear, or if you have a complex fistula with multiple tracts.

These may include:

Your surgeon may also do a more detailed physical examination of your anus if necessary. You’ll have an anaesthetic for this. It may be done under general anaesthesia, which means you’ll be asleep or regional anaesthesia, which means the lower part of your body will be numb. Your surgeon may be able to treat you during this examination under anaesthesia (EUA) – they’ll explain what could be done during your procedure.

About anal fistula surgery

There are different types of surgery to treat an anal fistula – see the ‘Types of anal fistula surgery' section below for information on these. All types of surgery for anal fistula aim to get rid of the fistula, while causing as little damage to the sphincter muscles around your bottom (anus) as possible. These muscles allow you to control when you poo, so if they’re damaged, it can result in a loss of control (incontinence).

After your surgeon has assessed you, they’ll talk to you about your treatment options, the risks and benefits of each, and what they recommend for you. This will depend on where exactly your fistula is and whether it involves any of the sphincter muscle.

Your surgeon will explain exactly what will happen during the procedure, what to expect afterwards and the risk of potential complications. Be sure to ask any questions you have, and ask for more time to make a decision if you need it. If you’re happy to go ahead with the procedure, you’ll be asked to sign a consent form – so it’s important to make sure you understand everything.

Preparation for anal fistula surgery

Your surgeon will explain how to prepare for your anal fistula surgery. For example, if you smoke, they’ll ask you to stop, as smoking increases your risk of getting a wound or chest infection, and your wound won’t heal as well.

Your operation will usually be done under general anaesthesia, which means you’ll be asleep during the operation. Some procedures for anal fistula can also be done using regional anaesthesia. This means you’ll be awake during the operation, but the lower part of your body will be numb.

After your operation, you’ll usually be able to go home the same day. Ask family or a friend to drive you home and stay with you overnight.

If you’re having a general anaesthetic, you’ll need to stop eating and drinking a few hours before your procedure. Follow the advice you get from your anaesthetist or doctor. If you have any questions, just ask.

On the day of your procedure, your surgeon will meet with you to check you’re well and still happy to go ahead. The staff at the hospital will do any final checks and get you ready for surgery. You may need to wear compression stockings, for example, or have an injection of an anticlotting medicine to help prevent deep vein thrombosis (DVT). The DVT preventive measures you have will be specific to you and your surgeon will explain what you need.

Types of anal fistula surgery

Fistulotomy

The most common type of operation for simple fistulas is a fistulotomy. This involves opening up the fistula so that it can heal from the inside out.

Once your anaesthetic has taken effect, your surgeon will put a probe (a thin metal instrument) into the opening of the fistula to help them find the fistula. This will help them to decide what type of treatment is best for you. For most fistulas, they’ll then cut through your skin and underlying tissues, to open up the top of the fistula. They’ll leave the wound open (they won’t use any stitches) so that it can gradually heal. This type of operation works well for the majority of fistulas (if they aren’t complex).

Other options for complex fistulas

Occasionally you may need a different type of treatment. This is more likely if your fistula passes through more of your sphincter muscle, you have several fistulas, or if your fistula keeps coming back.

If, when your surgeon assesses you, they find you have a complex fistula, they’ll usually use a seton to drain the track and keep the fistula under control. A seton is a small thread that your surgeon will put through your fistula before any other procedure. Some people just continue to have treatment with setons over the long term, without going on to have any further procedures. If you may need more complex treatment, your surgeon may refer you to a specialist in treating complex fistulas.

Other types of surgery include the following.

  • Staged fistulotomy. This is when you have several operations over a number of months, to open up the fistula a little at a time. Your surgeon will put a loose seton around the remaining fistula each time to help drain it until your next operation.
  • A cutting seton. This is a specific type of seton that gradually cuts through the sphincter muscle, and opens up the fistula and allows scar tissue to form behind. This reduces the risk of incontinence.
  • Anal advancement flaps. This involves creating a ‘flap’ of tissue within your anal canal, which is sewn down over the fistula opening. It avoids your surgeon needing to cut through your sphincter muscle.
  • Plugs, glues and pastes. These can be inserted or injected into your fistula to block it and help it to heal. There isn’t much good evidence to show that these work – but they are another option to avoid cutting your sphincter muscle. Your doctor may recommend trying it as part of a research trial.
  • LIFT procedure (ligation of the inter-sphincteric fistula tract). This surgery is for fistulas that pass through the sphincter muscles. It involves closing up one end of the fistula before cutting the fistula open, between your sphincter muscles.
  • Endoscopic ablation. This procedure involves passing a tiny camera along the fistula and using an electrode to burn away tissue inside the fistula, before sealing it up.
  • Laser therapy. In this procedure, laser therapy is used to destroy and seal the fistula. There’s limited evidence on how well it works.

Aftercare for anal fistula surgery

You’ll need to rest until the effects of the anaesthetic have passed. You’re likely to have some discomfort as the anaesthetic wears off, but your hospital team will offer you pain relief. If you have any problems peeing after your surgery, you may need a catheter at first (a tube that drains pee (urine) from your bladder).

Once you’re ready, your nurses will encourage you to get up and move around. This will help to prevent complications. You can begin to drink and eat when you feel ready.

You’ll usually be able to go home on the day of your surgery. But ask someone to drive you home and stay with you overnight. Having a general anaesthetic can really take it out of you. You might find that you're not so co-ordinated or that it's difficult to think clearly. This should pass within 24 hours. In the meantime, don't drive, drink alcohol, operate machinery or make any important decisions.

Before you go home, you’ll be given some advice about caring for your wounds, signs of infection to look out for and pain relief you can take. You’ll also be told what the arrangements are for follow-up in the clinic.

Recovering for anal fistula surgery

You’re likely to have some discomfort for a week or so after anal fistula surgery. You can take over-the-counter painkillers such as paracetamol or ibuprofen if you need pain relief. Constipation can be common after surgery. Your surgeon may recommend that you take a laxative to soften your poo and help to reduce any discomfort. Always read the patient information leaflet that comes with your medicine and if you have any questions, ask your pharmacist for advice.

Your wound should heal within about six weeks. Depending on the size of your wound, you may need to go back to hospital daily to allow them to change the dressings, to help keep it clean and heal. Your surgeon will let you know how long you’ll need dressings for. You might find it helpful to put a gauze pad in your underwear for the first week or two to protect your clothes from any discharge from your wound.

Have a bath or shower two or three times a day to help ease pain and discomfort, as well as to keep your wound clean. Don’t add anything to the bath water as this may irritate your wound. Dry the area carefully afterwards.

Your surgeon will give you advice about driving, going back to work, having sex and getting back to your usual activities and routine. This is usually after a few days.

Complications of anal fistula surgery

Complications are when problems happen during or after the operation. The possible complications of any operation include things like infection, bleeding or an unexpected reaction to the anaesthetic. Specific complications of anal fistula operation include the following.

  • Bowel incontinence. You may have sudden urges to poo that you can't control, sometimes just when you pass wind. The risk of this happening is different for different types of procedure. When your surgeon assesses you before your surgery, they’ll advise which type of operation is best to minimise the risk of this happening.
  • Your wound may take longer than usual to heal.
  • The fistula may come back. The chance of this happening varies between different procedures. You may need a different type of operation if it comes back.
  • Narrowing (stenosis) of your anal canal – the end of your bottom. This can happen as your fistula starts to heal and can make it difficult to poo. Your doctor may prescribe medicines to help with this.

Frequently asked questions



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  • Reviewed by Rachael Mayfield-Blake, Freelance Health Editor, January 2022
    Expert reviewer Mr. Nick Reay-Jones, Consultant Surgeon General Surgery
    Next review due February 2025

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